Without exception, cholesterol gallstone is more common among women than men in every population studied. This consistent and conspicuous gender difference starts during puberty, continues throughout the childbearing years, but fades alter menopause. Biliary sludge, a newly described ultrasonographic diagnosis, is a mixture of cholesterol monohydrate crystals and other precipitates within the gallbladder, and it is regarded as a precursor form of gallstones. Sludge is frequently found in pregnant women, although the risk factors for the development of gallbladder sludge and stones during pregnancy have not been clearly defined. The investigators propose a prospective investigation of gallstones and biliary sludge that develop during pregnancy to accomplish several specific aims. First, they will determine the incidence rate of biliary sludge and gallstones during pregnancy and compare this rate to a nonpregnant control sample. Second, they will look for factors predictive of the development of biliary sludge gallstones during pregnancy, including obesity, age, hyperinsulinemia, hyperlipidemia and serum estradiol and progesterone levels. Lastly, they will examine predictors of persistent gallstones and biliary sludge disease in the postpartum period by following women until one year after delivery. They aim to include as many as 7,280 women in this study. They will be recruited from the prenatal and genealogy clinics of Madigan Army Hospital. Development of gallstones and biliary sludge will be defined by ultrasonographic examination of the gallbladder contents performed at pre-specified intervals during gestation and postpartum, and at an equivalent time in the non-pregnant control group. A variety of analytic methods will be used to achieve these specific aims of this study. Gallstone and biliary sludge are common in women and represent major causes of morbidity. The investigators state that this study will add new and important insight into the risk factors leading to these outcomes and affecting their natural history. They further note that this information, in turn, may lead to effective strategies for treatment and prevention of these conditions.